beforeDestroy is called in Vue 2 before the instance is destroyed and is used to clean up event listeners, timers, etc. 1. Run after all subcomponents have been destroyed; 2. The instance is still fully available at this time; 3. Suitable for manually cleaning content that Vue does not process automatically, such as global events, timers, WebSocket connections; 4. Unlike destroy, the latter is called after the component is completely destroyed; 5. Common uses include removing window event listening, clearing timers, and unsubscribing services; 6. Be careful not to add responsive attributes or performing time-consuming operations here, and make sure to cancel asynchronous tasks to avoid errors.
In Vue 2, the beforeDestroy hook is called right before a Vue instance is destroyed. This happens after the instance is fully functional but just before it starts tearing everything down—like removing watchers, child components, and direct bindings.
This lifecycle stage gives you a chance to do any necessary cleanup, like removing event listeners or canceling async operations that might still be running.
When exactly does beforeDestroy run?
The beforeDestroy lifecycle hook runs after :
- All child components have been destroyed.
- The Vue instance is still fully functional (you can still access data, methods, etc.).
It's the perfect time to manually clean up things that Vue doesn't automatically handle, such as:
- Event listeners added outside of Vue (eg, with
window.addEventListener) - Timers (
setTimeout,setInterval) - WebSocket connections
- Any third-party libraries that need explicit teardown
At this point, the component is about to be torn down, so anything you want to remove or reset should be done here.
How is beforeDestroy different from destroyed?
Here's how these two hooks compare:
-
beforeDestroy: Called just before destruction begins. Component is still active. -
destroyed: Called after the component has been fully destroyed. Everything has been cleaned up by Vue.
Once you're in destroyed , most of the component's internal systems are already gone. So if you need to reference component data or call methods, do it in beforeDestroy .
Practical use cases for beforeDestroy
A few common scenarios where beforeDestroy comes in handy:
-
Unbinding global events : If you added an event listener on
windowordocument, you should remove it here.beforeDestroy() { window.removeEventListener('resize', this.handleResize); } Clearing times : Prevent memory leaks by clearing any pending timeouts or intervals.
beforeDestroy() { if (this.pollingTimer) { clearInterval(this.pollingTimer); } }Cleaning up subscriptions : If you're using a pub/sub system or connecting to external services, make sure to unsubscribe or disconnect.
Things to keep in mind
- Don't add new reactive properties here — it won't work.
- Avoid doing heavy computings unless absolutely necessary.
- Make sure any async tasks (like API calls) are cancelled to prevent errors when trying to update a non-existent component.
Also, remember that once the instance is destroyed, it can't be reused. So if you're caching references or storing state elsewhere, now's the time to wrap that up cleanly.
Basically that's it.
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